Effects of cyclosporin A, gentamicin and furosemide on rat renal function: a lithium clearance study

1. This study applied clearance methods of inulin, lithium, potassium, sodium and para-aminohippuric acid (PAH) for investigation of the effects of cyclosporin A (CyA), furosemide and gentamicin on rat (n = 92) renal function. The drugs were dosed for 2 weeks; CyA 12.5 mg/kg per day, gentamicin 32 mg/kg per day and furosemide 5 mg/kg per day. 2. The questions asked were: could these methods differentiate the effects of drugs with different sites of action, and would gentamicin or furosemide exaggerate the nephrotoxicity of CyA? 3. Furosemide increased sodium clearance (CNa) 74% and fractional sodium clearance (FENa) 105%, while fractional sodium reabsorption in the distal nephron (FDNR) was reduced, compared with placebo-treated controls. 4. Gentamicin reduced CPAH 29% and Cin 37%, while FENa increased 335%. Proximal fractional reabsorption (PFR) and absolute proximal reabsorption (APR) decreased. 5. CyA depressed CPAH 32% and lithium clearance (CLi) 56%, and increased PFR. 6. The effects of CyA and furosemide in reducing renal function were not additive. 7. CyA plus gentamicin reduced CPAH to 35% of the value in untreated controls, equal to 52% of the CPAH of CyA-treated rats; Cin was reduced to 46% of the Cin of CyA-treated rats. 8. Rats given CyA, furosemide and gentamicin had decreased Cin, CPAH and CLi compared with rats given either CyA plus furosemide or gentamicin plus furosemide. 9. Thus, in this investigation of drugs known to have different sites of actions, the differences in renal and tubular function were discernible with the lithium clearance method. 10. The nephrotoxicities of CyA and of gentamicin were additive, while furosemide did not aggravate CyA nephrotoxicity.